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1. S-QGPU: Shared quantum gate processing unit for distributed quantum computing

   https://doi.org/10.1116/5.0241972  

   Du, Shengwang; Ding, Yufei; Qiao, Chunming (March 2025, AVS Quantum Science)

   We propose a distributed quantum computing (DQC) architecture in which individual small-sized quantum computers are connected to a shared quantum gate processing unit (S-QGPU). The S-QGPU comprises a collection of hybrid two-qubit gate modules for remote gate operations. In contrast to conventional DQC systems, where each quantum computer is equipped with dedicated communication qubits, S-QGPU effectively pools the resources (e.g., the communication qubits) together for remote gate operations, and, thus, significantly reduces the cost of not only the local quantum computers but also the overall distributed system. Our preliminary analysis and simulation show that S-QGPU's shared resources for remote gate operations enable efficient resource utilization. When not all computing qubits (also called data qubits) in the system require simultaneous remote gate operations, S-QGPU-based DQC architecture demands fewer communication qubits, further decreasing the overall cost. Alternatively, with the same number of communication qubits, it can support a larger number of simultaneous remote gate operations more efficiently, especially when these operations occur in a burst mode. 

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2. Photocurrent detection of the orbital angular momentum of light

   https://doi.org/10.1126/science.aba9192  

   Ji, Zhurun; Liu, Wenjing; Krylyuk, Sergiy; Fan, Xiaopeng; Zhang, Zhifeng; Pan, Anlian; Feng, Liang; Davydov, Albert; Agarwal, Ritesh (May 2020, Science)

   Applications that use the orbital angular momentum (OAM) of light show promise for increasing the bandwidth of optical communication networks. However, direct photocurrent detection of different OAM modes has not yet been demonstrated. Most studies of current responses to electromagnetic fields have focused on optical intensity–related effects, but phase information has been lost. In this study, we designed a photodetector based on tungsten ditelluride (WTe 2 ) with carefully fabricated electrode geometries to facilitate direct characterization of the topological charge of OAM of light. This orbital photogalvanic effect, driven by the helical phase gradient, is distinguished by a current winding around the optical beam axis with a magnitude proportional to its quantized OAM mode number. Our study provides a route to develop on-chip detection of optical OAM modes, which can enable the development of next-generation photonic circuits. 

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3. Entanglement of nanophotonic quantum memory nodes in a telecom network

   https://doi.org/10.1038/s41586-024-07252-z  

   Knaut, C M; Suleymanzade, A; Wei, Y-C; Assumpcao, D R; Stas, P-J; Huan, Y Q; Machielse, B; Knall, E N; Sutula, M; Baranes, G; et al (May 2024, Nature)

   Abstract A key challenge in realizing practical quantum networks for long-distance quantum communication involves robust entanglement between quantum memory nodes connected by fibre optical infrastructure^1–3. Here we demonstrate a two-node quantum network composed of multi-qubit registers based on silicon-vacancy (SiV) centres in nanophotonic diamond cavities integrated with a telecommunication fibre network. Remote entanglement is generated by the cavity-enhanced interactions between the electron spin qubits of the SiVs and optical photons. Serial, heralded spin-photon entangling gate operations with time-bin qubits are used for robust entanglement of separated nodes. Long-lived nuclear spin qubits are used to provide second-long entanglement storage and integrated error detection. By integrating efficient bidirectional quantum frequency conversion of photonic communication qubits to telecommunication frequencies (1,350 nm), we demonstrate the entanglement of two nuclear spin memories through 40 km spools of low-loss fibre and a 35-km long fibre loop deployed in the Boston area urban environment, representing an enabling step towards practical quantum repeaters and large-scale quantum networks. 

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4. Floquet Engineering Topological Dirac Bands

   https://doi.org/10.1103/PhysRevLett.129.040402  

   Lu, Mingwu; Reid, G. H.; Fritsch, A. R.; Piñeiro, A. M.; Spielman, I. B. (July 2022, Physical Review Letters)

   We experimentally realized a time-periodically modulated 1D lattice for ultracold atoms featuring a pair of linear bands, each with a Floquet winding number. These bands are spin-momentum locked and almost perfectly linear everywhere in the Brillouin zone: a near-ideal realization of the 1D Dirac Hamiltonian. We characterized the Floquet winding number using a form of quantum state tomography, covering the Brillouin zone and following the micromotion through one Floquet period. Last, we altered the modulation timing to lift the topological protection, opening a gap at the Dirac point that grew in proportion to the deviation from the topological configuration. 

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5. Efficient Distribution of Quantum Circuits

   https://doi.org/10.4230/LIPIcs.DISC.2021.41  

   G_Sundaram, Ranjani; Gupta, Himanshu; Ramakrishnan, C R (January 2021, Schloss Dagstuhl – Leibniz-Zentrum für Informatik)

   Gilbert, Seth (Ed.)

   Quantum computing hardware is improving in robustness, but individual computers still have small number of qubits (for storing quantum information). Computations needing a large number of qubits can only be performed by distributing them over a network of smaller quantum computers. In this paper, we consider the problem of distributing a quantum computation, represented as a quantum circuit, over a homogeneous network of quantum computers, minimizing the number of communication operations needed to complete every step of the computation. We propose a two-step solution: dividing the given circuit’s qubits among the computers in the network, and scheduling communication operations, called migrations, to share quantum information among the computers to ensure that every operation can be performed locally. While the first step is an intractable problem, we present a polynomial-time solution for the second step in a special setting, and a O(log n)-approximate solution in the general setting. We provide empirical results which show that our two-step solution outperforms existing heuristic for this problem by a significant margin (up to 90%, in some cases). 

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